I have just purchsed a newish house with space for an loft conversion. In the original build the main consumer unit has a 40 amp MCB marked sockets. A single line out to the loft is in place (but not connected!) and the cable is capable of carrying at least 40A.
I reckon that the builder planned to install a secondary consumer unit in the loft and run a ring main and lighting circuit out of this unit with the loft from protected by the 40A MCB on the main unit. Is the acceptable under building regs?